System And Method For Operating An Engine With Reduced NOx Emissions

ABSTRACT

A method for reducing NOx emissions during operation of an internal combustion engine in commerce which, when burning hydrocarbon fuel as a primary fuel, in the absence of any secondary fuel, has a characteristic stoichiometric ratio. The method includes: in the absence of electrolytic activity, providing and entraining a quenching species in a gaseous medium; and then interacting the quenching species with constituents present during oxidation of the primary fuel in a combustion chamber of the engine.

BACKGROUND AND SUMMARY OF THE INVENTION

Vehicle emissions, such as CO, CO₂, SOx, NOx and particulate matter (PM)have significant health and socioeconomic impacts while efforts tomitigate these continue to create significant economic burdens on manyindustries. Despite significant improvements in many metropolitanregions since the implementation of clean air standards, there remaincontinued demands for further emissions reductions to improve health andwelfare. However, as emissions standards become more stringent, the costof compliance is expected to become more burdensome, with growingconcern that compliance can adversely affect engine performance.Further, equipment capable of providing compliance with existingrequirements is subject to high maintenance and reliability problems, attimes causing disruption in the engine operation.

Emission levels of air pollutants from engines may be optimized underlimited conditions, e.g., for emissions certification tests, withouttesting in other engine operating ranges, such as high rpm, high load,highly transient high output operation, and prolonged low-loadoperation. As a result, it can be expected that emissions levels duringreal-world driving can be higher than the levels observed during limitedcertification tests.

Air pollutants in vehicular emissions are commonly controlled withexhaust gas recirculation (EGR) systems which re-use exhaust gases tomanage the composition of the air-fuel mix during combustion. Typically,EGR systems recirculate gases from the exhaust manifold through the airintake manifold to reduce oxygen concentration in the combustionchambers 18, effectively rendering the mixture fuel rich. Therecirculated exhaust gases entering the air intake manifold may rangefrom 10 percent to over 50 percent.

Use of EGR to reduce NOx operation is premised on the theory that, withrelatively rich fuel content in the combustion chamber, the combustionreaction is shifted further below the stoichiometric ratio, thisreducing the combustion temperature to a level below the thermal NOxgeneration temperature. Whereas the EGR approach can result in about afifty percent net reduction in NOx emissions, other sources of NOx, suchas prompt NOx, become important contributing sources of pollutants underthese conditions.

EGR operation causes increased heat rejection as the amount ofrecirculated exhaust increases, requiring a larger cooling system. Also,with exhaust gas recirculation diluting the volume percent of oxygenentering the engine from the intake manifold, the engine power densityexpectedly decreases. Consequently, more soot is generated and moreunburned hydrocarbons are carried out the exhaust. Thus, an effort tolimit NOx emissions results in elevation of another type of emission.With regulatory limits on both particulate matter and unburnedhydrocarbons, efforts to reduce NOx have made it necessary toincorporate additional equipment in the engine exhaust system. Theseequipment add-ons can be of limited efficacy. For example, some dieselparticulate filters only remove about eighty five percent of theparticulate matter in the exhaust gases. The EGR systems may requireadditional components to overcome or offset the aforementioneddrawbacks. Moreover, EGR systems cannot, alone, provide sufficient NOxemission reductions to comply with many current and future emissionsrequirements.

Due to the aforementioned drawbacks of EGR systems, other strategies toreduce NOx emissions, such as, selective catalytic reduction (SCR) havebeen developed for diesel engines. SCR systems inject an aqueoussolution of urea into the exhaust flow in the presence of a catalyst toconvert the NOx into molecular nitrogen and water. Treatment of exhaustgases by catalytic reduction, in combination with EGR, has enabledengine operations to comply with current regulatory requirements. Yetthese supplemental NOx reduction systems are mechanically and chemicallyfragile. They present reliability problems which can create disruptionsto the flow of commerce. There is continued need for more reliablemethods and equipment operation for mitigating NOx production in dieselengines. Further, as emissions limits become more stringent, there is aneed for new mitigation solutions.

Ideally, alternate means for reducing NOx emissions should completelysupplant the need for EGR systems and not create side effects whichadversely affect engine performance or require additional controlequipment. In one series of embodiments, the present invention providesa reliable chemical method for controlling generation of NOx bysuppressing a primary mechanism of NOx formation.

It has been observed that modest reductions in NOx emissions areachievable by shifting from a fuel-rich AFR relative to thestoichiometric point to provide a fuel-lean combustion. As noted in thecontext of EGR systems, in the past this has adversely affected thequality of the combustion, resulting in substantial losses in power andincreased emissions of hydrocarbons.

U.S. Pat. No. 9,388,749, now incorporated herein by reference, teachesthat, with a gaseous secondary fuel present in the cylinders, adverseeffects of reducing the fuel-to-air ratio are less severe than whenrunning the engine without the secondary fuel. Consequently there is anexpanded range of acceptable air-to-fuel ratio from which an optimumratio can be selected to improve fuel economy and or lower NOxemissions. A feedback control loop may be provided to use a parameter inan algorithm which generates an adjustment value to mitigate NOxemissions. The control loop may also be used to adjust the measuredparameter by modifying an input variable, e.g., the air-to-fuel ratio.Weighting functions may be assigned to determine relative influence ofmultiple control loops. The weighting functions may vary temporally orbased on engine operating conditions, including ambient states.

A method according to one embodiment of the present invention moregenerally provides for addition of an adduct to the air-fuel mixture.After entering the combustion chambers of a combustion ignition (CI)engine, the components of the adduct disassociate to provide a freenitrogen quenching species to mitigate NOx formation. When combined withaddition of a species of Reactive Hydrogen that undergoes oxidation inthe combustion chamber, reductions in NOx emissions, on the order of 75%or more are attainable during operation of TDI diesel engines.

Of the several species of nitrogen oxides (NOx) emitted duringhydrocarbon fuel combustion, NO₂ is known to have the most adverseeffects on health. High concentrations of NO₂ cause inflammation of theairways and reduced lung function. More generally, NOX contributes tothe formation of secondary airborne inorganic particulate matter (PM)and atmospheric ozone (O₃). There is a need to provide improved ways toreduce NOx emissions levels which reduce mitigation costs as well as thelevels of emissions.

SUMMARY OF THE INVENTION

In one embodiment a method is provided for reducing NOx emissions duringoperation of an internal combustion engine in commerce which, whenburning liquid hydrocarbon fuel as a primary fuel, in the absence of anysecondary fuel, has a characteristic stoichiometric ratio. The methodincludes providing a free nitrogen quenching species for interactionwith constituents present during oxidation of the primary fuel in acombustion chamber of the engine while operating the engine at anair-to-fuel ratio greater than the characteristic stoichiometric ratio.

In another embodiment of a method is provided to actively control outputof OH⁻ entrained gas, from a secondary gas production system, with anengine management system comprising an engine control unit (ECU), themethod comprising selecting different look-up tables or sets of datavalues based on engine operating conditions to vary secondary gasproduction to decrease NOx emissions and optimize fuel consumption undermultiple engine operating conditions.

A method is also provided for programming an Electronic Control Unit foran engine based on sensor data gathered to define each in a plurality ofsets of engine control settings, also referred to as defining look-uptables, to assign sets of values of variables for use in enginemanagement and secondary gas generation. The method includes (i)determining, based on collected sensor data, sets of values for each ofmultiple different engine operating conditions to minimize NOx emissionsbased on inputting a variable amount of a secondary gas into acombustion chamber of the engine, and (ii) selecting a set of values toapply to an operating condition based on sensor data acquired indicativeof the operating condition, the different sets of values including dataproviding different AFR values based on different engine operatingconditions and the values in different sets including differentsecondary gas generation rates. Also according to the invention anembodiment of a method is for reducing NOx emissions during operation ofan internal combustion engine which, when burning hydrocarbon fuel as aprimary fuel, in the absence of any secondary fuel, has a characteristicstoichiometric ratio. The method includes (i) providing a free nitrogenquenching species in an aqueous solution, (ii) entraining the quenchingspecies in a secondary gas by either aerating the solution with a gas orby passing the gas through the solution where providing and entrainingoccur in the absence of electrolytic activity that would produceReactive Hydrogen from water molecules. The secondary gas is injectedinto a combustion chamber of the engine while operating the engine at anair-to-fuel ratio greater than the characteristic stoichiometric ratiofor interaction of the quenching species with constituents presentduring oxidation of the primary fuel.

According to still another embodiment, a method is provided for reducingNOx emissions during operation of an internal combustion engine incommerce which, when burning hydrocarbon fuel as a primary fuel, in theabsence of any secondary fuel, has a characteristic stoichiometricratio. The method includes: in the absence of electrolytic activity,providing and entraining a quenching species in a gaseous medium; andthen interacting the quenching species with constituents present duringoxidation of the primary fuel in a combustion chamber of the engine.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 schematically illustrates a Turbocharged Direct Injection (TDI)diesel engine and an associated dual fuel control system;

FIG. 2 illustrates reductions in NOx emissions achievable with the TDIengine of FIG. 1, as a function of AFR values greater than thestoichiometric ratio for diesel fuel; and

FIGS. 3 and 4 illustrate a functional relationship between flow rate ofReactive Hydrogen injected as a secondary gas into the engine of FIG. 1and the suppression of NOx emissions.

FIGS. 5 and 6 are flow diagrams of an ECU monitoring engine stateconditions and applying data from look-up tables to control engineoperations; and

FIG. 7 is a flow diagram illustrating an ECU operating in aself-training mode.

DESCRIPTION OF THE INVENTION

Before describing in detail the particular methods and systems andcomponents relating to embodiments of the invention, it is noted thatthe present invention resides primarily in a novel and non-obviouscombination of components and process steps. So as not to obscure thedisclosure with details that will be readily apparent to those skilledin the art, conventional components, connections and steps have beenomitted or presented with lesser detail, while the drawings and thespecification describe in greater detail other elements and stepspertinent to understanding the invention. Further, the followingembodiments do not define limits as to structure or method according tothe invention, but provide examples which include features that arepermissive rather than mandatory and illustrative rather thanexhaustive.

FIG. 1 schematically illustrates a multi-cylinder engine system 6comprising an exemplary emissions control system 8 configured foroperation with an exemplary multi-cylinder Turbocharged Direct Injection(TDI) combustion ignition (CI) diesel engine 10. The emissions controlsystem 8 includes a gas production module 94 which provides a secondarygas 90 as an input to the engine combustion chambers 18. In oneembodiment the gas production module 94 may be based, in whole or part,on a design which generates reactive hydrogen by performing electrolysisof water present in a KOH aqueous solution provided in a tank 96, asdescribed in U.S. Pat. No. 9,388,749. In certain embodiments the aqueoussolution is referred to as an electrolytic bath.

Other embodiments of the gas production module 94 generate a freenitrogen quenching species. That is, in a chemical reaction thatdestroys the activity of a primary reactive species, e.g., freenitrogen, by combining it with a secondary species, creation of the newcombined tertiary species renders the reactive species in thecombination inactive. When the primary reactive species is freenitrogen, the secondary species, referred to as a quenching species, maybe reactive hydrogen, e.g., OH⁻. The free nitrogen quenching species maybe provided with minimal or no electrolysis. In such implementations thegas production module 94 may include a pump 98 which injects air oranother gas into the tank 96. With, for example, the tank containing theKOH solution, OH⁻ and water present in the KOH solution may becomeentrained in a flow of the secondary gas 90 travelling through thesolution and into the combustion chambers 18.

In an exemplary method for reducing NOx emissions during operation ofthe engine 10 burning petrodiesel as a primary fuel, a free nitrogenquenching species interacts with constituents present during oxidationof the primary fuel in the combustion chamber 18. The engine may beoperated at an air-to-fuel ratio greater than the characteristicstoichiometric ratio (e.g., 14.9) and a secondary gas 90 injected intothe combustion chamber may be a result of electrolysis or may otherwisebe based on entrainment of a free nitrogen quenching species. The freenitrogen quenching species may be an electron donor species selectedfrom the group consisting of OH⁻ (e.g., OH⁻ present in a KOH solution),amines (R₃N where R═H, CH₃ or C₂H₅), and quaternary ammonium hydroxide(R₄NOH where R═CH₃ or C₂H₅, etc.). The free nitrogen quenching speciesmay be a reactive nitrogen chelating metal (M), where M is a Group IAmetal, a Group 2 metalor is selected from the group consisting of Mg,Be, Zn, Cd, B, Al, Ga, In, Zr, Ti, Sn and Cu, Li and Na. The illustratedembodiments suppress formation of one or more NOx species (e.g., NO,NO₂, N₂O , N₂O₂, N₂O₃, N₂O₄) in the CI engine 10 while operating withpetrodiesel as the primary fuel, although other embodiments of theinvention may be applied to a variety of internal combustion enginetypes (e.g., spark ignition (SI) and turbine engines) and with a varietyof other primary fuel types, including gasoline, other petroleumdistillates, and synfuels, including those synfuels derived from biomassor gaseous hydrocarbons.

The engine 10 comprises an engine fuel system 12 and an air intakesystem 14, several components of which are shown in relation to theengine 10. The engine includes a series of combustion chambers/cylinders18, one of which is shown in the side view of the engine 10 shown inFIG. 1. An Engine Control Unit (ECU) 20 receives data on engine stateconditions from a plurality of sensors to determine how the engineelectronic control system operates. The ECM also stores the calibrationvalues that define rated horsepower, torque curves, and rpmspecifications.

Through sensor readings, the ECU 20 applies direct measurements of stateconditions to determine, for example, fuel delivery rate and AFR. Moregenerally, the ECU 20 generates a series of command signals (e.g., forcontrol of fuel pump pressure, secondary gas generation output rate,fuel injector operation and air intake pressure) to control engineoperation. The ECU also monitors engine operating variables (e.g.,Throttle Position, RPM, fuel rail pressure) and settings (e.g., crankposition and cam phase). Sensor values are monitored to indicate:exhaust gas temperature sensor S₂₂ values SS₂₂, manifold absolutepressure (MAP) sensor S₂₄ values SS₂₄, exhaust pressure sensor S₂₆values SS₂₆, and barometric pressure sensor S₂₈ values SS₂₈. The systemalso includes sensor S₃₀ monitoring intake air temperature values SS₃₀,monitoring O₂ sensor S₃₂ values SS₃₂ in the exhaust gases and monitoringthe Mass Air Flow (MAF) values SS₃₄ with sensor S₃₄.

For a given load demand, the ECU 20 issues command signal C40 and C42 tocontrol injection of current and/or injection of gas into the productionmodule 94. The command signal C40 adjusts pulse width modulation tocontrol current through switching MOSFETs in current control circuitryof the module 94. In turn, this controls the output level of secondarygas, generated by electrolysis, comprising reactive hydrogen. Commandsignal C42 adjusts input of gas from the pump 98 into the tank 96 tocontrol the rate of production of the secondary gas comprising aquenching species as further described herein. The ECU 20 also generatescommand signals to adjust combustion parameters, including commandsignal C46 which adjusts the fuel injector pulse width. Upon sensingdemand for more fuel via a throttle position sensor signal STPS₅₀,generated from a throttle position sensor TPS₅₀ (not shown), commandsignals C52 are sent from the ECU 20 to the driver module 56 of a fuelpump 58 to adjust fuel pressure P62 output from the pump to the fuelrail 66 to feed the fuel injectors 70. The ECU monitors pressure signalsSS74 generated by a fuel pressure sensor S74 (not shown) positioned atthe fuel rail 66 near the injectors 70 to control the response of thefuel pump 58 by varying command signals C52 input to the fuel pumpdriver module 56 accordingly. The ECU also generates command signals C46to control injector timing and pulse width to meet sensed engine loaddemands and attain a desired Air-to-Fuel Ratio (AFR). Fuel rail pressuremay vary based on the timing of the injection pulse.

The ECU monitors and adjusts crank position and cam phase as a functionof load (e.g., through look up tables) to create a valve timing overlapby which both the intake and exhaust valves are open together. Thisallows the remaining gas to be scavenged, thereby reducing combustionchamber temperatures to further suppress thermal NOx production.

The illustrated fuel control system differs from conventional systems byproviding electronic control of NOx emissions as a function of operatingconditions. In this example, the fuel control system also adjusts thevolumetric flow rate of a secondary gas 90 input to the combustionchambers 18. The secondary gas 90 may comprise an adduct molecule whichflows through the air intake manifold to the cylinder chambers 18. Inone embodiment, the adduct molecule comprises a quenching species thatdisassociates from the molecule when subjected to high temperatures.

In one embodiment, the adduct may be an aggregate of different chemicalspecies, held together by weak forces such as hydrogen bonding or vander Waal bonding. The adduct may then be a H₂O. OH⁻ aggregate in whichthere are weak bonds between the oxygen atom in the OH⁻ anion and thetwo hydrogen atoms in the water molecule This adduct dissociates underhigh temperature conditions during oxidation of the primary fuel in thecombustion chamber to provide OH⁻ species capable of mitigating NOxformation. The secondary gas 90 may be a secondary fuel furthercomprising one or multiple species of Reactive Hydrogen. The ReactiveHydrogen species may include an oxidant or a fuel component. On theother hand, the secondary gas 90 may simply comprise the adductentrained in air. The air may contain water vapor.

The term Reactive Hydrogen as used herein and in the claims meansproducts which contain atomic hydrogen (H) or molecular hydrogen (H₂) orhydrogen in the form H⁺, OH⁻, O⁻H⁺ or H₂O₂ suitable for use in aninternal combustion engine to facilitate performance and mitigation ofNOx generation when burning a primary fuel such as petrodiesel. TheReactive Hydrogen may be a component of the secondary gas 90 while thesecondary gas contains other components such as H₂O. When the gaseousproduct is generated by electrolysis the product generally includesoxygen where the ratio of hydrogen to oxygen is 2:1 and the combinationof constituents is referred to as oxyhydrogen or HHO. Although disclosedembodiments of the invention include hydrogen generation systems whichproduce one or more species of Reactive Hydrogen, the secondary gas 90may comprise a pre-prepared secondary fuel containing Reactive Hydrogen.In specific embodiments, a hydrogen generation system may produceReactive Hydrogen in situ in the presence of heat and a catalyticmaterial such as copper. For example, a light hydrocarbon such asmethane may be passed through a variable number of heated copper tubesto provide a supply of Reactive Hydrogen. The process may involvegeneration of a plasma or thermal cracking or a uv photoelectricprocess.

The effects of the several species of Reactive Hydrogen on controllingemissions is not easily predicted, in part because any of multiplechemical mechanisms can influence the outcome, depending on the reactionconditions. Optimum conditions must be determined in order to obtain thebeneficial effects of adding the Reactive Hydrogen species to theoxidant-fuel premix. For example, HHO is, in part, an oxidant.Introducing HHO into the intake air manifold results in higher oxidantconcentration, which leads to leaner mixtures and reduced flametemperatures. Addition of Reactive Hydrogen species into the combustionchamber gas mixture is believed to change the fuel combustion mechanismsat the atomic level, and alter complex pollutant formation dynamics. HHOwill not always reduce NOx and in some circumstances will increase NOxgeneration. In fact, there can be a sharp increase in NOx emissions whencylinder temperature exceeds the threshold temperature (around 1100° C.)for NOx formation. Yet, under specific circumstances identified throughexperimentation, the NOx emission levels can be reduced by the presenceof certain Reactive Hydrogen species.

Proportional changes in one or multiple input variables, e.g., changesin concentration of the quenching species or the Oxidant to Fuel Ratio(OFR) can optimally minimize generation of NOx emissions. The fuelcontrol system illustrated in FIG. 1 is programmable to optimize engineperformance while reducing the NOx emissions, or to minimize the NOxemissions while sustaining acceptable engine performance, e.g., powerand fuel efficiency. In principle, the engine system 6 comprising anemissions control system 8, can minimize generation of NOx emissionswhile operating the engine at a fuel-lean AFR, e.g., a ratio greaterthan about 14.9 for the TDI engine 10, recognizing that the effectiveOFR is influenced by presence of oxidant and fuel species of ReactiveHydrogen sent into the combustion chamber as part of the secondary gas90. On the other hand, the emissions control system 8, while operatingwithout generating fuel species of Reactive Hydrogen, can also adjustthe engine to a fuel-lean AFR, and vary other parameters, including thevolumetric flow rate of the secondary gas 90 and the level of ExhaustGas Recirculation (EGR) to minimize generation of NOx emissions. Ineither case, based on other data, such as exhaust gas temperature, thesystem may be programmed to adjust variables such as AFR or OFR toreduce combustion temperatures and thereby prevent generation of NOx bythermal NOx mechanisms.

The fuel control system adjusts proportions of oxidant (or air) and fuelto enhance suppression of the NOx emissions when at least the quenchingspecies component interacts with nitrogen in the combustion chamber.

Referring to FIG. 1, the air intake system 14 may be coupled to receivea secondary gas 90 comprising a Reactive Hydrogen quenching specieswhich, for example, may be an OH⁻ link which disassociates from theadduct. The exemplary OH⁻ species interacts with, for example, one ormultiple combustion intermediates to facilitate driving the fueloxidation toward a more complete burn. The quenching species ties upreaction intermediaries (e.g., N atoms or nitrogen-containing radicals)to limit production of NOx species and enable the more completeoxidation of the carbonaceous fuel. The quenching mechanism appears tobe particularly effective in mitigating thermal NOx production.

For embodiments in which the gas production module 94 generates productsof water electrolysis, it is believed the OH⁻ becomes entrained in theflow of the secondary gas generated in the module and acts as aquenching species to limit formation of NOx. When the source of thesecondary gas 90 is an aqueous solution of the quenching species,through which there is a gaseous flow, such as air or another gasbubbled through the reservoir by the pump 98, only water vapor and theadduct comprising the quenching species in the reservoir may becomeentrained as constituents in the flow of the secondary gas 90. Movementof air or other gas into the aqueous solution is generally referred toas a gaseous flow, which can refer to bubbling of gas into the solutionor aeration.

The invention departs from conventional emissions control by enablingcontrol over the generation of nitrogen oxides and thereby reducing thecostly burden of add-on mitigation equipment typically required forvehicle compliance, which equipment reduces combustion efficiencies orimposes costly after-combustion solutions. Rather, comparativemeasurements of vehicle performance for embodiments of the inventionindicate that a reliable chemical process may be introduced in thecombustion chamber to suppress the formation of one or plural NOxspecies.

Operation of methods according to the invention is not limited to aparticular theory. Yet, discussion of one potential explanation of how aquenching species might effectively mitigate NOx emissions may provideinsight for optimally mitigating NOx emissions. Consideration is givento the relative importance of three distinct mechanisms for NOxformation in CI engines. Generation of NOx emissions begins at the startof the chain of combustion reactions with these mechanisms, which arecommonly referred to as thermal NOx, prompt NOx, and fuel NOx.

Thermal NOx is formed by high-temperature chemical reactions. Theprincipal reactions governing the formation of thermal NOx frommolecular nitrogen, referred to as the Zeldovich mechanism, are:

O+N₂→N+NO   (1)

N+O₂→O+NO   (2)

Prompt NOx formation is associated with the CH-radical. During fuelcombustion, CH radicals readily react with molecular nitrogen to formHCN, which then reacts quickly to form NOx, as shown in reaction 3:

HCN+O₂+N→NO, NO₂, CO₂, H₂O, trace species   (3)

Fuel NOx becomes a significant pathway when the fuel containsorgano-nitrogen compounds as described by the reaction of Equation (4):

R_(x)N+O₂→NO, NO₂, CO₂, H₂O, trace species   (4)

In an effort to more completely mitigate NOx emissions, multiplecombustion process variants were evaluated for possible effectiveness inlimiting NOx generation resulting from a combination of the Thermal NOxmechanism and the prompt NOx mechanism. Functional dependencies weremeasured during operation of two different 2.0 Liter TDI diesel engines.FIG. 2 illustrates observed reductions in NOx emissions as a function of

-   (i) AFR values greater than the stoichiometric ratio for diesel    fuel, i.e., greater than approximately 14.9, as a control, without    introducing any species of Reactive Hydrogen or other quenching    species;-   (ii) entrainment of hydroxyl radicals (OH⁻) in a secondary gas 90,    created by bubbling air from the pump 98 through the tank 96, with    no electrolysis, and injecting the air into the combustion chambers    18, while varying AFR among values greater than the stoichiometric    ratio for the diesel fuel; and-   (iii) entrainment of hydroxyl radicals (OH⁻) and multiple other    species of Reactive Hydrogen created by electrolysis (e.g., oxygen    and atomic or molecular hydrogen), in a secondary gas 90 sent into    the combustion chambers 18, while varying AFR among values greater    than the stoichiometric ratio for diesel fuel.

Curve (i) of FIG. 2 illustrates an asymptotic decrease in NOx emissionsas AFR values were increased relative to the stoichiometric ratio forthe diesel fuel, i.e., while holding the volumetric flow rate of fuelinto the engine constant and without introducing any Reactive Hydrogenspecies. The NOx emissions dropped by up to about 45 percent as the AFRincreased relative to the stoichiometric ratio. However, the reductionsin NOx emissions, as AFR was increased, were accompanied by reducedengine power and increased generation of soot). Curve (ii) of FIG. 2illustrates an asymptotic decrease in NOx emissions similar to that ofCurve (i) where, in addition to providing a constant volumetric flowrate of fuel into the engine, hydroxyl species present in the combustionchambers 18 drive fuel oxidation further toward a complete burn at anAFR ranging from values greater than 16 to at least 25. Curve (iii) ofFIG. 2 illustrates still another asymptotic decrease in NOx emissionswhere a constant volumetric flow rate of primary fuel is provided intothe engine and, in addition to providing hydroxyl radicals in thecombustion chambers 18, a secondary fuel, HOH generated in the gasproduction module 94 by electrolysis, provides non-carbonaceous oxidantand fuel in the combustion chambers 18 while varying the AFR amongvalues greater than 16 to at least 21. With both the entrained hydroxylradicals and the secondary fuel being input to the combustion chambers,the NOx emissions dropped by up to about 75%.

The portion of the evaluation performed under conditions of providing noReactive Hydrogen input to the cylinders 18, as a control, indicatesthat NOx emissions can be suppressed in an engine operating with aprimary fuel by adjusting the AFR to be more fuel lean relative to thestoichiometric ratio. Providing a quenching species such as OH⁻ in thecombustion chambers 18 results in further suppression of NOx emissionsthan that observed under the control conditions corresponding to Curve(i) of FIG. 2 but, advantageously, it was also found that power outputof the engine increased substantially, e.g., to a range comparable tothat observed when the AFR is fuel-rich. In limited testing, providingthe quenching species without electrolysis (as per Curve (ii) of FIG. 2)and a Reactive Hydrogen species with water electrolysis (per Curve (iii)of FIG. 2) were each found to further suppress NOx emissions to levelslower than observed when operating under the control conditionsresulting in the data in Curve (i) of FIG. 2. Further, application of aquenching species without electrolysis and application of a ReactiveHydrogen species with water electrolysis both have been found to providefurther NOx reductions as a function of the operating temperature of theaqueous tank solution. At least over a limited range, the NOx emissionswere reduced as a function of increasing the temperature of the aqueoussolution in the tank. In one embodiment, the temperature of an aqueoussolution in the tank 96 can be elevated with a thermostaticallycontrolled tank heating system 100 that provides, for example, heatedfluid from the engine coolant system for circulation about the aqueoussolution. The tank heating system 100 is schematically indicated in FIG.1 by a heating coil wrapped about the tank 96. In some instances thelevel of NOx may initially decrease as temperature of the electrolyticbath increases and, after reaching a minimum, increase with increasingtemperature.

With a conventional engine arrangement, having no injection of secondarygas 90 into the combustion chamber 18, the NOx emissions were reduced byup to 45 percent by shifting the AFR to values greater 14.9. Withinjection of secondary fuel at a fixed rate of 1.2 standard liters perminute (slm), the NOx emissions dropped by up to about 75% when thesecondary gas 90 comprised HHO.

FIGS. 3 and 4 illustrate suppression of NOx emissions as a function ofthe amount of secondary fuel comprising Reactive Hydrogen, injected asthe secondary gas 90, into the air-intake manifold of the same TDIengine for which NOx emissions data of FIG. 2 were acquired. TheReactive Hydrogen species included both oxidant and non-carbonaceousfuel (e.g., in the form of HHO). The NOx levels were found to initiallydecrease as the injection rate of the secondary fuel increased, by atleast 40 percent more than observed for the control illustrated as curve(i) in FIG. 2. For the TDI engine this effect was observed as the rateof secondary fuel injection increased from zero up to 1.2 slm. Beyondthe fuel injection rate of 1.2 slm, significant declines in the NOxemissions level were not observed and at 1.5 slm an increase in the NOxemissions level was observed.

The data of FIGS. 1 and 2 confirm that, based on the combination ofinjecting HHO comprising Reactive Hydrogen and entrained OH⁻ into thecombustion chamber, and varying the Air to Fuel Ratio (AFR), theemissions level can be optimized across the range of fuel demand levelsby up to 75 percent or more. In addition to there being a temperaturedependence on generation of the secondary gas 90, both with and withoutelectrolysis, the volume of Reactive Hydrogen (liters per minute)produced with the gas production module 94 can be increased by injectinga gas into the tank with the pump 98.

Although operation according to the invention is not dependent onunderstanding of a specific theory, the described reduction in NOxemission levels, irrespective of engine speed, may, at least in part, bedue to suppression of thermal NOx production. Cyclic formation of atomicnitrogen species per Equations (1) and (2) may be contained to limit NOxgeneration. The afore described presence of OH⁻ during combustion maylimit the regenerative reaction sequence of equations (1) and (2), whichsequence would otherwise continue production of N and NO as per theZeldovich mechanism. Providing hydroxyl radicals during hydrocarbonoxidation in the combustion chamber may create a major sink for atomicnitrogen that terminates NOx formation chain reactions as shown inEquation (5):

N+OH→H+NO   (5)

In this sense, hydroxyl radicals may act as the quenching species. Byentraining an adduct comprising OH⁻ when the cell reservoir tank 96contains, for example, an aqueous solution of KOH, NOH, NaOH or NH₄OH inwhich case the adduct may be H₂O.OH⁻, with the secondary gas 90 enteringthe engine air intake manifold, the adduct is carried into thecombustion chamber where the OH disassociates from the adduct moleculeand interacts with atomic nitrogen per Equation (5).

If NOx suppression is based on such a quenching mechanism, the NOxemissions may be limited but not eliminated completely, e.g., to theextent Prompt NOx production and Fuel NOx production mechanisms are notaffected by quenching agents.

In order to fully describe the operation of the engine according to theinvention, a brief review of engine operating conditions is provided.The ECU 20 manages the fuel injectors by referencing a library ofresident “look-up” tables to know what to do under each and everyoperational condition. In the light load mode, with the engine at“normal” operating temperature, the engine may operate in a closed loop,using the oxygen sensor output data to determine the fuel injection ratefrom the fuel look-up tables, to afford optimum power.

Adaptive feedforward control is a common approach for handlinguncertainties and time-varying effects, such as in automotive controlapplications. The adaptation of the feedforward controller is oftencombined with a linear feedback controller. The feedforward controller(usually in the form of look-up tables) is used to overcome thenonlinearities that are due to variations of the operating point, whilethe feedback controller is used to manage fast disturbances. If theengine behavior is changing, for example due to stacked tolerances, thefeedforward controller using the look-up table data, provides anadaptive function; and the ECU can routinely modify the inputs from thelookup tables to compensate for tolerance stacking. Tolerance stackingarises because engine parts are manufactured within tolerances to theideal measurement, and all these variations from ideal specificationsmay add up. The ECU must also routinely modify the inputs from thelook-up tables to compensate for engine wear and tear, variations infuel quality, and variations in ambient/atmospheric conditions. Howeverthere is a lag between the feedback controller and the adaptation of thefeedforward controller which can create phase shifts that must bedecoupled to avoid instabilities in the control system. Ideally, thedecoupling method should not depend on the structure of the feedforwardcontroller (i.e., the structure of the look-up tables); nor should itdepend on the method of the adaptation.

As shown in the flow diagrams of FIGS. 5 and 6, the ECU 20 monitorsengine state conditions and engine loadings via the throttle positionsensor TPS₅₀. The state conditions include the air pressure, density,and temperature in the intake manifold which, when combined with otherinformation (such as NOx emission level, changing loads, and driverdemands), enables the ECU 20 to identify from a look-up tablepre-determined, but possibly suboptimal, AFR and secondary gas injectionrates. These values are expected to provide desired levels of improvedengine performance while assuring that NOx emissions levels comply withpredetermined limits. Data made available to the ECU through the look-uptables can be acquired by exercising the engine through a series ofloading based on dynamic operating conditions. For example, noting thatboth engine power and optimal NOx reduction are influenced by severalengine-related dependent variables (e.g., exhaust gas temperature, O₂levels in the exhaust gases, manifold absolute pressure (MAP), exhaustpressure, intake manifold air temperature, Inlet Air Temperature (beforeturbocharge), Mass Air Flow (MAF) and barometric pressure), a set ofindependent variables are adjusted for individual engine operatingstates, including transient states, to identify values of the variablesin the set which yield optimum performance, including minimum emissionsunder individual operating conditions. Optimum performance may requiretradeoffs between, for example, any of fuel economy, engine power andNOx emissions levels for each operating state. The set of independentvariables includes AFR, adjusted by changing PWM signals which controlfuel injection, the amount of secondary gas input to the combustionchamber and the level of Exhaust Gas Recirculation (monitored with anEGR Differential Pressure Sensor). The operating conditions may includeall operating modes of the engine system 10, including normalaccelerations, cruise steady state conditions through the range ofoperating speeds, and variable road conditions such as when hillclimbing is performed in a high gear (e.g., between 40 mph and 60 mph).Thus, the data stored in the look-up tables provide real-time adjustablesettings known to provide acceptable or desirable performance during thewide range of dynamic operating conditions. The values of the settingsare based on prior determinations of how, collectively, each independentvariable in the set is can be controlled for an acceptable or optimumpredetermined level of performance.

Then, in addition to use of look-up tables to determine AFR andsecondary gas injection rates, fuel settings (e.g., injector pulsewidth) and intake air settings (e.g., manifold pressure), the emissionscontrol system 8 can refine the secondary gas injection rate to optimizethe power and fuel economy, subject to achieving predetermined NOxemissions limits. As indicated in FIG. 6, the system can make adetermination of NOx emissions compliance (based on sensor readings) andreadjust the control settings to both meet emissions limits andoptimized engine performance.

The “closed loop” look-up tables, providing varied AFR and secondary gasinjection rates, may be optimized for minimum NOx emissions withoutcompromising engine performance relative to that which is achievablewith control systems which operate with a constant AFR and no secondarygas injection. These table values may be continuously updated byoperating the engine control system in an unsupervised machine learningmode, as shown in FIG. 7. While monitoring state conditions and engineloading, the process begins with use of initial look-up tables which maycontain minimal data. New data for fuel-oxidant mixtures that affordpredetermined pollutant levels are captured and validated based onadaptive phenomenological models that relate engine performance andpollution emissions to engine settings such as air to-fuel ratios,engine speed (rpm), air density in the intake manifold, secondary gasproduction rates, changing loads, engine tolerance characteristics,driver demands, etc. to refine the models. The ECU 20 operates in a modewhere settings can be initialized. Then the ECU is trained according toan adaptive machine learning algorithm model by providing a learningalgorithm with training data to learn from. The results from theanalyses are automatically added to the look-up table. The lookup tablesand feedback control mechanism according to the invention also apply toengine conditions which do not require providing any secondary gas inorder to comply with the NOx emissions or optimum power generation.

FIGS. 8 through 10 illustrate performance of the emissions controlsystem 8 under a hill climb simulation performed on an 18 wheel tractortrailer accelerating from 40 MPH to 70 MPH while in the highest of thetransmission gears. In the acceleration mode, the fuel pressure wasmaintained at 28000 psi, the fuel injection duty cycle was independentlyset to 80% (i.e., 30 ms pulse width during the entire acceleration), andthe EGR was independently set at 26% duty cycle. All other variableswere set by ECU from look up tables. An aqueous solution of KOH in thetank 96 was at 30 C, to produce a constant flow of Reactive Hydrogen atthe rate at 3.5 slm. In each of the figures, the dashed line curveillustrates NOx emissions during maximum acceleration of the vehiclewhile the engine 10 consumes only primary fuel in accord withconventional regulation of AFR by the ECU 20. No use of ReactiveHydrogen or other secondary gas was input to the engine. In each of thefigures the solid line curve illustrates NOx emissions during maximumacceleration of the vehicle powered with the same primary fuel whilereceiving Reactive Hydrogen as a secondary fuel into the combustionchambers 18. Both the secondary fuel and AFR for primary fuel wereadjusted for reduced NOx emissions, e.g., based on data relating toengine dependent operating variables. The tank solution temperature was30 C.

Referring to FIG. 7, the NOx emissions levels are shown to increase withtorque in a linear manner. Notably the NOx emissions for the solid linecurve, corresponding to injection of a secondary fuel, has a shallowercurve than does the dashed line curve. FIG. 6 illustrates that duringthe majority of the acceleration, e.g., between 40 MPH and 60 MPH, theemissions control system suppresses the emissions level substantially,at times by more than 1,000 ppm.

Features of the invention have been illustrated for engines having OEMelectronic control systems, and are especially suitable to systemshaving ECM's which use tale look-up data to optimize engine performance.In one series of embodiments, such engines may be equipped with customversions of data accessed by an electronic control module tocooperatively operate an emissions control system without compromisingengine performance. provide one or more of the functionalities whichhave been disclosed.

While the invention has been described with reference to particularembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention.Accordingly, the scope of the invention is only limited by the claimswhich follow.

1. A method for reducing NOx emissions during operation of an internalcombustion engine in commerce which, when burning liquid hydrocarbonfuel as a primary fuel, in the absence of any secondary fuel, has acharacteristic stoichiometric ratio, the method comprising: providing afree nitrogen quenching species for interaction with constituentspresent during oxidation of the primary fuel in a combustion chamber ofthe engine while operating the engine at an air-to-fuel ratio greaterthan the characteristic stoichiometric ratio.
 2. The method of claim 1where the primary fuel predominantly comprises petrodiesel fuel and theair-to-fuel ratio range is greater than 14.9.
 3. The method of claim 1where the primary fuel predominantly comprises petrodiesel fuel and theair-to-fuel ratio ranges between 15-25.
 4. The method of claim 1 wherethe NOx emissions are controlled as a function of engine loading byvarying a parameter taken from the group consisting of AFR, rate ofinjecting a secondary gas comprising the quenching species, cam phasing,crank position relative to cam shaft, fuel rail pressure, injectionpulse width, mixture of air and exhaust gas based on EGR valve settings,and electrolytic bath temperature for secondary gas generation.
 5. Themethod of claim 1 where the free nitrogen quenching species is carriedinto the combustion chamber in an adduct.
 6. The method of claim 1 wherethe free nitrogen quenching species is an electron donor speciesselected from the group consisting of OH—, amines (R₃N where R═H, CH₃ orC₂H₅), and quaternary ammonium hydroxide (R₄NOH where R═CH₃ or C₂H₅,etc.) or the free nitrogen quenching species is a reactive nitrogenchelating metal (M), where M is a Group IA metal, or is selected fromthe group consisting of Mg, Be, Zn, Cd, B, Al, Ga, In, Zr, Ti, Sn, Liand Na.
 7. The method of claim 1 where the free nitrogen quenchingspecies is a hydroxyl radical carried into the combustion chamber in anadduct.
 8. The method of claim 7 where the hydroxyl radical is providedby entrainment in air passing through an aqueous solution comprisingKOH, NaOH or NH₄OH.
 9. The method of claim 1 where the quenching speciesis entrained in a secondary gas passing through an air intake manifoldand into the combustion chamber.
 10. The method of claim 9 where thesecondary gas is emitted from an aqueous solution.
 11. The method ofclaim 10 where the quenching species is placed in solution with waterand is entrained as a constituent of the secondary gas as a gas passesthrough the aqueous solution.
 12. The method of claim 1 where thequenching species is placed in an aqueous solution and entrained in asecondary gas by passing air through the solution in the absence ofelectrolytic activity that produces Reactive Hydrogen from watermolecules.
 13. The method of claim 12 wherein the secondary gascomprises air, water vapor and OH⁻.
 14. The method of claim 9 where thesecondary gas comprises a secondary fuel which is oxidized with theprimary fuel in the combustion chamber.
 15. The method of claim 14 wherethe secondary fuel being provided to the combustion chamber comprisesReactive Hydrogen which is formed in an electrolytic cell while theengine is operating.
 16. The method of claim 1 wherein the free nitrogenquenching species is provided by entraining a moiety, obtained from anaqueous hydroxide species, in a gaseous medium comprising oxygen. 17.The method of claim 1 where the free nitrogen quenching species is ahydroxide derived from an inorganic source.
 18. The method of claim 17where the hydroxide species comprises a Group 1 metal or a Group 2metal.
 19. The method of claim 17 where the hydroxide species isintroduced as an alkaline solution of sodium aluminate (a.k.a., Bayerliquors). 20-40. (canceled)